The present invention relates to a new and improved method and apparatus for casting articles. Although the method and apparatus can be used for casting many different types of articles, it is advantageously used for the casting of airfoils from nickel-chrome super alloys. The airfoils may be cast with a single crystal, equiaxed, or columnar grain crystal structure.
Airfoils which are used in gas turbine engines have previously been cast from nickel-chrome super alloys. The specific nickel-chrome super alloy used in casting the airfoil depends upon the desired characteristics for the airfoil. However, the nickel-chrome super alloy may have a composition generally similar to that disclosed in U.S. Pat. Nos. 3,260,505 or 4,371,404.
Ceramic molds formed by the lost wax process have previously been used to cast nickel-chrome super alloy airfoils. These ceramic molds are preheated to a relatively high temperature in a furnace. A super heated molten metal is then poured into the preheated molds.
The mold is then lowered from the furnace and cooled. As the molten metal in the mold cools, an airfoil having a desired crystal structure is formed. The furnace may have a construction generally similar to that shown in U.S. Pat. Nos. 3,841,384; 3,895,672; 3,897,815; and 4,178,986. It has been suggested that the mold could be immersed in a body of liquid coolant as it is withdrawn from the furnace in the manner disclosed in U.S. Pat. Nos. 3,763,926 and 4,108,236.
In an effort to obtain economical production, molds have been poured in clusters or groups. When this is done, the molten metal flows from a pour cup through a runner system to individual molds arranged in a circular array about the pour cup. It has also been suggested that individual molds could be moved along a horizontal path through a furnace to sequentially cast articles in the manner shown in U.S. Pat. No. 3,677,324.
In order to improve the characteristics of a cast article, it has been suggested that inert particles could be dispersed in molten metal in a mold by the use of ultrasonic waves in the manner disclosed in U.S. Pat. No. 3,678,988. In practicing the method disclosed in this patent, a tube is inserted into the mold. The inert particles are carried through the tube into the molten metal by a flow of gas. After the particles have been dispersed within the molten metal, the tube is withdrawn and ultrasonic vibrations are set up in the molten metal. The molten metal is then solidified.